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JE LABS 2A3 amplifier

MartinV56

MartinV56

Well-Known Member
Hello to all the members of this forum. For some time I have been coming caressing the idea to be constructed an amplifier 2A3 JE Labs. Some of you has listened and is familiarized with this simple single ended triode amplifier. I obtained the circuit in internet. Welcome suggestions and friendly commentaries of the friends of this forum, thanks, Martín :thmbsp:

http://members.myactv.net/~je2a3/simple45.htm
 
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I studied that project for a long time, and would like to build it myself someday. I don't think you could go wrong, as long as you use some good iron. As far as the 2A3 tube in general, I haven't found anything I like better, for all around music listening. If you do build it, please keep us posted as you progress, and good luck, Jay
 
Jay, thanks, as it is progressing in the project I will be telling to them. I have thought about copying the U-808 Tango for which. I will try to use the best iron, great or oriented and the best wire than it can obtain, again thanks and I will inform to them into the progresses of the project, Martin
 
Hello, this is the project of the 2A3. Chasis finished and painted, sockets, connectors, switch, pilot and potetiontemeter installed, great chassis part of the internal wiring, the next week when give me the transforming and chocke I install this items. When the 2A3 vacuum tubes arrive to me from Tube Depot, begins the tests of this project, best regards and thanks, Martin
PD. This circuit is not the JELabs, is other.

photos:


 
Very nice (professional) looking work Martin. I am a big fan of "chicken head" knobs myself.:thmbsp: Is this your first amp building project? Jay
 
Hey!!!,
I just helped build that very project with a friend from work. He'd built a nice wood chassis, assembled the parts and together we assembled and wired it up.

We did a few small mods to the circuit, like decreasing the 2A3's grid resistor to 100k from 330 or 470k. Also increased the coupling cap to .5 uF from .22uF. It sounds quite nice, and seems to make more power than 3W( anyway it sounds big ).

Installed Sovtek 2A3's, NOS Tongue-Sore 6SU7GTY. Used a Chinese 274B for the rectifier.
cheers,
Douglas
 
I like the Sovteks too:yes: and a question:D Could you explain (in simple terms) what effect the two changes you mentioned have? Thanks, Jay
 
Hey-Hey!!!,
I'd be glad to...:)

First the grid resistor value change. If we look at the RCA data sheet for the 2A3 it allows 500k for this value, and in the same paragraph says that it is best to use an inductance( either a grid choke, or an interstage TX secondary ). The grid *WILL* have some signal related current. It will be small for the most part, but it will be there. The bigger the resistor ref'ing it to ground the bigger the change in grid voltage due to such current.

Second, increased the coupling cap between the cathode follower section and the 2A3 grid. We just increased the load the cap must drive by shrinking the grid resistor, so in order to keep the LF response similar we increased the value of the cap. Remember it is the product R*C that determines this response. It isn't going to be the same, since we went down by 1/3 and up by 2...

Besides, little caps sound little I think.
cheers,
Douglas
 
Hello, thanks very much, Jay by your words, like Douglas. This it is not my first project, always I wanted to have a 2A3 and I have solved to do it, the circuito obtain in a page DIY, is very similar to the amplifier Sun 2A3, I have decided to use rectifying diodes instead of valve 5U4G, thank you very much and I will continue telling to them on the advances of the project, I hope to have good results with the output transformers that I have commanded to make a local craftsman, thanks again, Martin
 
Hi, here is the 2A3 amplifier, the next week come the 2A3 vacuum tubes from antique supply, I happy, Martin

photo

 
That looks very nice Martin. I'm curious as to what kind of capacitors you used? Maybe we could have an underneath picture. Please let us know how it sounds, and what speakers you will be using. Nice work, Jay
 
Hi, Jaymanaa, the good Dr. Stanley, capacitors they are not nothing of the remaining world , they are the ones it can get round here in Bogotá, they are from china , no than really soft-hearted quality , to the near project bring than Mouse Antique or Tube Depot The tubes than shopping they went the 2A3 than Valve Art. The loudspeakers than I have they are the next. Infinite Kappa 7.1 89 db 6 ohms remaining cast-off to the 2A3, a Altec Lansing Nine Series II 93db than the try with the SET and a old Elected Voice Baronet SP 12 they are really responsive and I think that they will be the ideals for this amplier, thanks Martin

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Hey! That's looking real nice, Martin! I've also decided to build this amp, using the schematic from Angela Instruments site. Is this the one you're putting together? I like the layout you've used, and will be curious to hear how it sounds with the Valve Art tubes.
 
Build with the input section on pins 4-5-6, and the cathode follower on 1-2-3. Then you'll be able to do some crazy stuff like trying 6EM7 or 6DN7 without any mods...:) Just make sure you can deliver the heater current( which the Hammond is quite capable of ).
cheers,
Douglas
 
Excellent, Pak... I'll take your advice to heart.:yes:

I'm thinking to use the James output trannies - they've apparently changed the way they name them, but I'm waiting for the 6112HS (2.5K/3.5K, 10W, 70mA) from Euphonia audio. It's out of stock at the moment, but in a couple of weeks...:naughty:
 
Hey!!!,
I am glad to see you using good Iron. I have come to the conclusion that if I were to build a SE amp of my own it would be with James output TX's.

Leave room under the hood, there's all sorts of interesting stuff you can try with that general set of parts...:) not to mention even greater levels of performance with some carefully done additions. Nothing really complicated, just some careful changes/mods.

Drop back in on this when the parts arrive.
cheers,
Douglas
 
I'm going all out and doing this the way they recommend - with Riken resistors and the Angela PIO coupling caps. It'll be by the book initially, but once it's built I'm likely to want to tinker with it...

BTW, I'm high on how much you can get for your money when you DIY, BABY! :banana:

Now, to keep my fingers crossed and hope it works...

(I better butt out of Martin's thread now - I think I've officially highjacked it.)
 
You will love the James iron redboy, I've heard it in many SET amps and used it in my 45/2A3, great stuff and I'll use it again.

Sorry to carry this thread-jack one post further Martin. :)
 
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